<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<div style="border: #1e55dc 1px solid;margin: 0 auto">
    <div class="b1"></div>
    <div class="b2"></div>
</div>
<div style="background-color: black;height: 200px">

</div>

</body>
</html>
<style>
    .b1{
        float: left;
        height: 200px;
        width: 300px;
        background-color: purple;
    }
    .b2{
        float: left;
        height: 200px;
        width: 200px;
        background-color: pink;
    }
</style>